This invention relates to an improved process for preparing chiral metallocene dihalides.
Chiral metallocene dihalides and derivatives are widely used as catalytic components in cocatalyzed polymerization reactions. In particular, transition metal-containing metallocene compounds are useful in conjunction with alumoxane cocatalysts in the polymerization of ethylene and the copolymerization of ethylene with 1-olefins or diolefins. Such catalyst systems are also useful in the production of isotactic polypropylene and other poly olefins.
Chiral metallocene dihalides such as ethylenebis(.eta..sup.5 -indenyl)hafnium dichloride and ethylenebis(.eta..sup.5 -indenyl)zirconium dichloride have been prepared by methods disclosed in Ewen et al., J. Am. Chem. Soc. 109: 6544 (1987) and Collins et al., J. Organomet. Chem. 342: 21 (1988), respectively, e.g., the deprotonation of 1,2-bis(3-indenyl)ethane with two equivalents of n-butyllithium followed by condensation with hafnium tetrachloride or zirconium tetrachloride. Although these prior art processes operate successfully, the yields are not optimum.
The process of this invention results in higher yields than the prior processes.